I expected to result below but actually not. I would like to know how to show the differences between two Collections. (objects are parent and child relationship) In this case, can I use standard method like removeAll() or can you recommend another approach like using apache-commons. Thanks.
CONSTRAINT
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1.Item.class is unmodifiable(eg. I can not add equals method)
2.If id is same between two objects, they are assumed as same things.
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EXPECTED
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removed object are:
2
same object are:
1
3
add object are:
4
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ACTUAL
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removed object are:
1
2
3
same object are:
add object are:
1
3
4
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package com.javastudy;
import java.util.ArrayList;
import java.util.List;
public class CollectionCompareToObjects {
public static void main(String[] args) {
List<Item> before = new ArrayList<Item>();
List<ItemEx> after = new ArrayList<ItemEx>();
before.add(new Item(1L));
before.add(new Item(2L)); // delete
before.add(new Item(3L));
after.add(new ItemEx(1L));
after.add(new ItemEx(3L));
after.add(new ItemEx(4L)); // added
List<Item> removed = new ArrayList<Item>(before);
removed.removeAll(after);
System.out.println("removed objects are:");
for(Item item : removed){
System.out.println(item.getId());
}
List<Item> same = new ArrayList<Item>(before);
same.retainAll(after);
System.out.println("same objects are:");
for(Item item : same){
System.out.println(item.getId());
}
List<Item> added = new ArrayList<Item>(after);
added.removeAll(before);
System.out.println("add objects are:");
for(Item item : added){
System.out.println(item.getId());
}
}
}
package com.javastudy;
public class Item {
private Long id;
public Item(Long id) {
this.id = id;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
}
package com.javastudy;
public class ItemEx extends Item {
private String name;
public ItemEx(Long id) {
super(id);
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}